Nowadays it has been proposed to mount a tire inflation pressure warning system to various vehicles that have wheels each including a rim and a tire assembled to the rim, such as passenger cars, buses, trucks, and motorbikes in order to constantly monitor the inflation pressure of the tire so that, if needed, an alert indicating abnormal situation of the tire inflation pressure is issued.
Tire inflation pressure warning systems generally include pressure sensors for measuring tire inflation pressure, and transmitters for wirelessly transmitting the measured inflation pressure, that are provided in tire cavity regions of the plurality of tires respectively. The tire cavity region, in this context, is a region surrounded by a tire inner circumference surface and a bottom surface of a rim bottom, to which air is filled. On the other hand, to the vehicle body side, a receiver for receiving the inflation pressure data wirelessly transmitted by the transmitters provided in the plurality of tires, and display means for informing the vehicle's driver of a tire status, according to the inflation pressure data acquired by the receiver are provided. In the receiver, the inflation pressure of the tire is constantly monitored to determine whether the inflation pressure is abnormal or not. In case of abnormal situation, an alert indicating that the tire inflation pressure is abnormal is issued to the vehicle's driver, through the display means.
In such tire inflation pressure warning systems, inflation pressure data is periodically transmitted from each transmitter provided in each of the plurality of tires. In this situation, there have been cases where data transmission timings from the transmitters overlap with each other, to cause interference of radio waves, resulting in data communication problems, and preventing the receiver from receiving the inflation pressure data normally.
PATENT DOCUMENTS 1-4 below describe examples of a tire inflation pressure warning system that solves the data communication problems which may be caused in a situation, as described above, where respective transmitters provided in respective tires transmit inflation pressure data respectively, and periodically.
PATENT DOCUMENT 1: JP2001-250186 A
PATENT DOCUMENT 2: JP 7-257119 A
PATENT DOCUMENT 3: JP 2001-322411 A
PATENT DOCUMENT 4: JP 2003-237328 A